In the case where a motor is driven by a motor drive device, if the insulation resistance of the coil (winding) of the motor is abnormally low, it is no longer possible to drive the motor normally. Because of this, a method for measuring the insulation resistance of a motor coil has been reported (for example, JP 2006-226993A, hereinafter referred to as “Patent Literature 1”). Patent Literature 1 describes a device that detects deterioration in the insulation resistance of a winding of a motor that is connected to a motor drive device including a power source unit configured to convert a three-phase alternating-current (AC) power source to a direct-current (DC) power source by rectifying the three-phase alternating current and smoothing the current by a smoothing capacitor, and a motor drive amplifier that drives a motor by converting the DC power source to an AC power source whose frequency can be varied.
In other words, when detecting deterioration in insulation resistance, the three-phase AC power source is cut off, one end of the smoothing capacitor is grounded, the other end is connected to the motor coil, and the current that flows through the insulation resistance of the motor is compared with a reference value, thereby, deterioration in insulation resistance is detected.
However, in order to accurately measure the insulation resistance of a motor, it is necessary to accurately measure the current that flows through the insulation resistance of the motor. If a failure occurs in the insulation resistance deterioration detection unit of the motor, an error occurs in the results of the measurement of the insulation resistance of the motor, therefore it is not possible to detect the error.
An object of the present invention is to “implement” a motor drive device that “detects a failure in an insulation resistance deterioration detection unit of a motor”, which has been the problem in the conventional technique, “without adding a dedicated detection circuit and increasing any unnecessary costs”.